As an example of parking assist system described above, an automatic steering control apparatus for a vehicle is known from Patent Document 1 identified below. This automatic steering control apparatus utilizes a power steering system and allows a parking operation using only an accelerator and a brake. The power steering system includes a switchover unit and a rotation control unit for rotating the steering wheel by a steering operation under stopped condition (so-called “zero-speed steering”). In the case of garage parking, the vehicle travels forward from a start position, with turning, and then upon passing a turning-direction switching position, the vehicle travels in reverse and is guided to a target position. Prior to initiation of its movement with turning, the vehicle is set with a necessary steering amount by a zero-speed steering, and then moves to a next position. Upon making stop at this position, the vehicle is set with a necessary steering amount again by means of a zero-speed steering operation. Patent Document 1: JP2003-341543 A (paragraphs 6, 10, 11, 18-26, etc.)
With the automatic steering apparatus or parking assist system disclosed in the above-described Patent Document 1, trouble for the driver in parking can be alleviated. However, the zero-speed steering operation using a power steering system is often problematic. For the automated steering, the power steering system is driven by an actuator (e.g. a motor). In the stopped condition, there is significant static frictional coefficient between the road surface and the wheels (tires), so that the a large torque is required by the actuator for driving the power steering system. Namely, the operation requires an actuator capable of much higher torque than that required by the normal power assisting function of the power steering system. This is undesirable as it leads to cost increase.
As a solution to this problem, it is conceivable to effect the automatic steering operation while the vehicle is in movement. In this case, no large torque is required for the power steering system. However, if an error occurs in the zero-speed steering operation by the driver, this error may lead to an error in the course of parking assistance.
The present invention has been made in view of the above-described situation. Its principal object is to provide a parking assist system capable of guiding a vehicle to a predetermined position irrespectively of a steering amount given prior to movement of the vehicle when the vehicle is guided with turning to the predetermined position under control of automatic steering, with the given steering amount.
For accomplishing the above-noted object, a parking assist system for assisting parking of a vehicle relating to the present invention, the system comprises:
a parking target position setting section for temporarily setting, at a predetermined stop position, a parking target position for the vehicle for each one of a plurality of parking modes;
a parking mode determining section for determining, after the setting of the parking target position and based upon an amount of steering operation effected by a driver, a parking mode and the parking target position corresponding to the parking mode;
a guiding section for guiding, by automatic steering control, the vehicle from the predetermined stop position to the parking target position along a guiding path including at least one turning-direction switching position; and
a correcting section for effecting such a correction that a deflection angle of the vehicle relative to the parking target position is corrected to a predetermined deflection angle at a corrected turning-direction switching position nearby said turning-direction switching position, regardless of the amount of steering operation effected prior to determination of the parking mode, the correcting section causing said guiding section to guide the vehicle to the parking target position, with the correction.
With the above-described characterizing feature, regardless of the amount of steering operation effected prior to movement of the vehicle, the vehicle is guided to the corrected turning-direction switching position nearby the turning point, under the automatic steering control. Further, as the correction is made such the deflection angle of the vehicle is corrected to the predetermined deflection angle at this corrected turning-direction switching position, when the vehicle moves from this corrected turning-direction switching position, the vehicle can follow a path parallel with the path initiating from the turning-direction switching position before the correction. As the corrected turning-direction switching position is nearby the original turning-direction switching position, it is possible to guide the vehicle to the parking target position with minimum amount of deviation.
In this way, with the inventive characterizing feature, it is possible to provide a parking assist system enabling guiding to a parking target position, regardless of a given amount of steering.
According to a further feature of the parking assist system of the invention, said correcting section causes said guiding section to guide the vehicle, with said corrected turning-direction switching position being a position of a same moving distance from the predetermined stop position as a moving distance from the predetermined stop portion to the turning-direction switching position.
With this characterizing feature, the total moving amount of the vehicle is maintained constant, so that there can be provided a preferred parking assistance according to the initially set guiding path.
Preferably, according to a further characterizing feature of the parking assist system, said guiding section effects a fixed steering control for guiding the vehicle with fixing the steering to a predetermined steering amount and a steering-back control for returning the steering amount to a neutral position at said turning-direction switching position; and                when the amount of steering operation provided at the time of determination of the parking mode does not agree to said predetermined steering amount, said correcting section effects a correcting control for either increasing or decreasing the amount of steering operation in the course of guidance from said predetermined stop position to the turning-direction switching position, so as to render the steering amount equal to the predetermined steering amount.        
As the parking assist system effects the guidance from the predetermined position to the turning-direction switching position, with fixing the steering, stable guidance can be provided. Further, if the correcting control for increasing or decreasing the steering amount in the course of this guidance, the steering amount can be returned to the predetermined steering amount speedily.
In the above, preferably, said correcting control is effected prior to said fixed steering control. With this, the steering amount can be returned to the predetermined steering amount speedily, and thereafter, the vehicle can be guided in a favorable manner by the stable fixed steering control.
Preferably, according to a further characterizing feature of the parking assist system of the invention, after said fixed steering control, the steering-back control for returning the steering amount to a neutral position at said turning-direction switching position is effected.
With the above, the steering amount at the corrected turning-direction switching position nearby the initial switching position prior to the correction, is returned to the neutral position. Therefore, the turning direction can be switched over in an advantageous manner.
Preferably, according to a further characterizing feature of the parking assist system of the invention, the steering amount per unit time in said correcting control is substantially equal to the steering amount per unit time in the steering-back control to the initial turning-direction switching position prior to the correction.
When the correcting control is effected during the guidance from the predetermined stop position to the turning-direction switching position, there arises need for the guiding section to guide the vehicle with switching the turning-direction switching position to the corrected switching position to make transition from the fixed steering control to the steering-back control. The corrected switching position needs to be nearby the initial switching position and the deflection angle of the vehicle relative to the parking target position needs to be the predetermined deflection angle. With execution of the correcting control, the guiding section needs to e.g. change the timing of transition from the fixed steering control to the steering-back control or change the moving distance of the vehicle from the predetermined stop position to the corrected switching position. In the course of this, if the steering amount per unit time in the correcting control is rendered substantially equal to the operation amount in unit time in the steering-back control to the corrected switching position, the required calculation can be easy. That is, it become advantageously possible to reduce the operation time or operation load for the guiding section.
According to a further characterizing feature of the parking assist system of the present invention, said parking mode determining section determines that the parking mode is a right-hand or left-hand garage parking if the steering was operated to the left or the right by an amount equal to or greater than a predetermined amount in the vicinity of the predetermined stop position; and said guiding path includes a forward guiding path including a turn in a first turning direction from said predetermined stop position to said switching position and a reverse guiding path including a turn in a second turning direction from said switching position to said parking target position.
In the case of a garage parking operation, in general, the vehicle is first driven obliquely forward with a turn in the opposite direction away from the parking target position. After the vehicle reaches the switching position, the vehicle is driven in reverse with a turn toward the parking target position. The first turn is the turn in the first turning direction and the second turn is the turn in the second turning direction. The mode of parking where the vehicle is first driven forward obliquely left-hand from the predetermined stop position is the right-hand garage parking. The mode of parking where the vehicle is first driven forward obliquely right-hand from the predetermined stop position is the left-hand garage parking. Therefore, based upon the amount of steering and the direction of steering, the parking mode determining section can effectively determine the direction of garage parking and then can determined the parking target position based upon the result of this determination.
The steering operation utilized for the above determination is in good agreement with the steering direction in moving forward the vehicle from the vicinity of the predetermined stop position. Therefore, the steering operation for the determination of parking mode can be effectively utilized for the forward guiding, so that it becomes possible to reduce the moving distance to the turning-direction switching position where reverse movement is started. Further, as the steering operation for the parking mode determination is same as the operation required for manual garage parking, the driver can effect input for commanding a parking mode in a natural smooth manner.
According to the above-described characterizing features, it has become possible to provide a parking assist system capable of guiding a vehicle to a predetermined position irrespectively of a given steering amount for providing highly efficient parking assistance.